The ATP synthase (F1-Fo, H+ATPase) is a multisubunit enzyme that utilizes the energy of the transmembrane H+ electrochemical gradient to drive the thermodynamic unfavorable synthesis of ATP. The molecular mechanisms underlying the transduction of electrochemical into the chemical energy of ATP are unclear at present. The long term objective of the present project is the elucidation of energy transduction mechanisms of ATP synthesis by mitochondrial ATP synthase. The primary focus of the present proposal is to elucidate the structure and function of Oligomycin sensitivity conferring protein (OSCP) and other stalk subunits in order to obtain some insights on their role in energy transduction. The specific aims include i) identification of domains of OSCP that are of structural and/functional importance, ii) elucidation of a) subunit interactions of OSCP and of b) possible conformational transitions in OSCP in specific response to energization, deenergization and uncoupling of mitochondria. These studies will be carried out using a combination of genetic engineering and physico-biochemical approaches.